Childhood Trauma and Borderline Personality Disorder Traits: A Discordant Twin Study

A discordant twin design was utilized to examine the potentially causal effects of childhood trauma (CT; i.e., emotional abuse, physical abuse, sexual abuse, and witnessing violence) on borderline personality disorder traits (BPD traits) in early adulthood. The participants were 2,808 twins between 17 and 23 years from the Oslo University Adolescent and Young Adult Twin Project. BPD traits were assessed by the Structured Interview for DSM-IV Personality (SIDP-IV), and CT was assessed using the Childhood Trauma Interview (CTI). BPD traits (h(2) = .50) and CT (h(2) = .33-.69) were both found to be moderately heritable. Small but statistically significant associations between CT and BPD traits were found in the total sample. After controlling for shared environmental and genetic factors in the discordant twin pairs, the analyses showed little to no evidence for causal effects of CT on BPD traits. The results indicated that the associations between CT and BPD traits stem from common genetic influences. These findings are inconsistent with the widely held assumption that CT causes the development of BPD. General Scientific Summary This study suggests that exposure to trauma in childhood and/or adolescence does not lead to later development of borderline personality disorder traits. Rather, the association between trauma and borderline personality disorder traits is better accounted for by shared genetic influences.